The present invention teaches that calcitonin gene-related peptide (CGRP), a neurotransmitter present in sensory nerves of several mammalian species, including humans, displays potent and efficient bronchoprotector and anti-inflammatory properties. More specifically, the present invention discloses that CGRP, when administered by inhalation to mammals, is capable of reducing the accumulation of eosinophils in the bronchial walls and of preventing bronchospastic airway responses, especially reversible airway hyperreactivity such as that encountered in bronchial asthma.
Bronchial asthma may be defined as a clinical syndrome characterized by outbursts of suffocation and of severe discomfort, especially when air is exhaled from the lungs. These asthma outbursts or asthma attacks often occur after exertions or during the night, are reversible either spontaneously or following treatments and are generally the result of bronchial obstructions. Three major factors contribute to these obstructions: a spasm (contraction) of the smooth muscles surrounding the airways, an inflammation of the bronchial walls accompanied by an effusion of fluid (oedema) and an hypersecretion of mucus. Although the relative contribution of each of these conditions is unknown, the net result is an increase in airway resistance, hyperinflation of the lungs and thorax, as well as abnormal distribution of ventilation and pulmonary blood flow. Thus, when an asthma attack occurs, breathing becomes difficult and may be accompanied by wheezing, coughing and dyspnea.
A major feature of this disorder is the propensity of the airways of asthmatics to respond in an abnormally exaggerated way (bronchial hyperreactivity) to a large variety of apparently unrelated stimuli such as allergic triggers, cigarette smoke, dust, pollens, chemical products, irritating vapours, cold air, food substances, physical exertion, stress, etc. Because of this increase in the sensitivity of the airways (10 to 1000 times normal), asthma has for a long time been regarded as a disease of the large airways which was believed to be caused mainly by mucus secretion and extensive narrowing of the tracheobronchi which consequently made breathing difficult for asthmatics.
This view started to change when morphometric studies on the bronchi of asthmatics revealed the presence of major inflammatory reactions within the mucosa of the bronchi. It is now recognized that another hallmark of this pathology is the massive influx of inflammatory cells, particularly eosinophils, in the bronchial walls and lung parenchyma. These cells are attracted to the airway mucosa by sequential processes involving adhesion molecules and a subset of helper T-lymphocytes designated Th2 that secrete an array of cytokines and chemokines. Eosinophils, for which the survival time is prolonged by these same cytokines, remain in the bronchial mucosa and release, among others, cysteinyl leukotriens, several hydrolytic enzymes, toxic mediators such as eosinophilic cationic protein and TNFxcex1 as well as Th2 cytokines, all of which cause further tightening of the airway smooth muscles cells and increased inflammatory reaction including increased eosinophilia. The importance of pulmonary inflammation to asthmatic response has been appreciated only recently but it is now well accepted that this inflammation paves the way for non-specific hyperresponsiveness and worsens airway obstruction.
Several subtypes of asthma have been identified during the last few years and it is estimated that in its different forms (i.e. allergic asthma and idiosyncratic asthma), this disease affects approximately 8 to 10% of the world""s general population, of which 5 to 10% are children.
If asthma attacks are mild, patients can take a medication (generally a bronchodilator) to suppress spasms (contractions) of the bronchi. If, however, attacks are severe and/or frequent, steroids can be added to the bronchodilator in order to reduce the inflammation occuring in the lungs. There are currently five types of remedies available on the market to treat asthma: (1) aerosol dosers (inhalators) which dispense bronchodilators, or agents that cause the relaxation of the bronchi (such as xcex22-adrenergic agonists administered with tiny delivery systems); (2) methylxanthines (such as theophylline), which are bronchodilators in tablet or capsule form; (3) corticosteroids (such as fluticasone or budenoside), used to reduce inflammation, available in aerosol, liquid or tablet form; (4) inhibitors of mast cell degranulation (i.e. chromones such as cromolyn sodium), most often used to prevent asthma triggered by physical activities, available either in tablet or aerosol form; and (5) antagonists of leukotrienes D4 and E4 (such as zafirlukast and montelukast), used as prophylactic substitutes to aerosol dosers, available in tablet form.
None of the medicines currently in use combines both bronchoprotector and anti-inflammatory properties. Additionally, none constitutes a cure for asthma, but each medicament can control its symptoms to varying degrees depending on the patient and/or the severity of his or her affliction. As a common feature, these medicines are comprised of synthetic or modified molecules and consequently, most cause secondary, undesirable effects, either at the moment of administration or following prolonged usage. For example, some xcex22-adrenergic agonists can bring about hand tremors, tachycardia and hypotension. Theophylline can induce nausea, diarrhea, headaches, muscle cramps, irritability, etc. Inhaling corticosteroids can irritate the vocal cords, resulting in hoarseness, as well as interfere with adrenal gland activity. They also induce several systemic effects such as elevated blood sugar, rounding of the face, changes in mood, high blood pressure, etc.
In view of the clinical importance of asthma, there is clearly an urgent need to identify new factors which can play a role in preventing, alleviating or correcting disfunctions such as inflammation and bronchial hyperactivity, such as those encountered in bronchial asthma. Thus, it is a feature of the present invention to prevent, reduce and/or alleviate the pathophysiological manifestations of asthma by the administration of a new and natural compound which combines both bronchoprotector and anti-inflammatory properties and which also has less undesirable side effects than those induced by the medicines now in use. It is another feature of the present invention to provide a method for the reduction and/or alleviation of the symptoms of asthma, by the use of a new therapeutic tool (i.e. CGRP) which is rapid acting and of relatively long duration.
Calcitonin gene-related peptide (CGRP) is a mammalian peptide containing 37 amino acid residues with a disulphide bridge between (Cys2 and Cys7. It is generated by tissue-specific RNA processing of the primary transcript of the calcitonin gene and is expressed mainly in thyroid parafollicular cells as well as in nuclei and nerve fibers of the central and peripheral nervous systems. In humans as in rats, this peptide is known to occur in two highly homologous forms, designated xcex1- and xcex2-CGRP, which differ in their primary sequence by one and three amino acids, respectively.
CGRP is widely distributed in the lung innervation of several mammalian species including humans. Peripheral branches of CGRP-containing nerve fibers are located beneath and within the airway epithelium, around blood vessels and seromucous glands, and within the smooth muscle layers of the tracheo-bronchial tree. Co-stored with substance P (SP) and neurokinin A (NKA) in primary afferent sensory neurons, CGRP is released (together with SP and NKA) from nerve endings upon capsaicin stimulation and after exposure to chemical irritants. Although the possible roles of this neurotransmitter in lung physiological and pathological processes are unknown, its production in the vicinity of bronchial smooth muscle cells led several investigators to suggest that CGRP could also affect (as do SP and NKA) adjacent tracheobronchial tone.
Numerous in vitro and in vivo investigations have been carried out with the aim of determining the role of CGRP on tracheobronchial smooth muscle cells. Although several of these studies have, to a large extent, focused on the putative myotropic activity of CGRP (i.e. contractile- or relaxant-induced responses), its main effect on airway smooth muscle tone still remains unclear, as considerable controversial data have been reported. For example, in human isolated airways, evidence has been provided for (1) and against (3) a bronchoconstrictor action of CGRP. Similarly, Luts and coworkers (5), Bhogal and coworkers (6), and Pinto and coworkers (7) showed that CGRP does not exert any contractile or relaxant effect in guinea pig trachea, whereas Hamel and Ford-Hutchinson (8) and Tschirhart and coworkers (9) reported that CGRP is one of the most potent contractile agents on guinea pig trachea yet identified. On the other hand, CGRP has been found to have no effect on hilus bronchi and parenchyma in the guinea pig in vitro (3, 7, 8) and to cause no changes in airway resistance in guinea pig in vivo (2, 3, 10-12).
More recently CGRP has been reported to potentiate the cholinergic contractions elicited by electrical field stimulation (EFS) in guinea pig trachea (7), to produce no bronchoconstriction in isolated and perfused guinea pig lung (13), to induce relaxations in guinea pig trachea precontracted with KCI and prostagiandin F2xcex1 (PGF2xcex1) (6), but to be without any relaxant effect in human and guinea pig bronchi precontracted with NKA (3) and in guinea pig trachea precontracted with histamine (7). In other animal species, CGRP has been shown to have no contractile effect on the airway smooth muscle in the rabbit (14), pig (15, 16), rat (4, 8), and mouse (17) in vitro and in sheep in vivo (18). Finally, CGRP has been noted to cause relaxations in pig trachea (15) and bronchi (16) precontracted with carbamylcholine and histamine, respectively, and in mouse airways precontracted with carbachol (17). Given this wide spectrum of reported pharmacological activities for CGRP, it may be easily understood that no investigator has really succeeded in ascribing a specific role for this neuropeptide with regard to its involvement in the regulation of airway smooth muscle tone. This issue has been in debate for some time in the scientific literature. Because no concensus has been reached yet, it is generally suggested that either the pharmacological effect of CGRP greatly differs between animal species and different levels of the tracheobronchial tree or that this sensory neuropeptide is related to pulmonary physiological processes other than those involved in the regulation of bronchomotor tone.
The present invention relates to the use of calcitonin gene-related peptide (CGRP) in the prevention, reduction and/or alleviation of the pathophysiological manifestations of asthma. The invention further concerns the use of active molecules (such as members of the calcitonin family of peptides i.e. CGRP, adrenomedullin, amylin, calcitonin and/or their respective functional derivatives; analogs and fragments) that are able to bind to the receptors that activate the intra and/or intercellular signaling pathways that mediate either or both the anti-inflammatory and bronchoprotective effects of CGRP in the lung.
The invention additionally pertains to an improved method for preventing or controlling ailments encountered in asthma (i.e. bronchial hyperreactivity and inflammation) which comprises administering to the host suffering therefrom an effective therapeutic amount of CGRP. The invention also provides improved means for preventing, alleviating and/or reducing bronchospastic airway responses characterized by reversible airway hyperreactivity by administering an amount of CGRP (or of its natural homologs and/or of their respective functional derivatives) sufficient to reduce airway hyperreactivity. In accordance with the foregoing, the invention also proposes a mode of administration having properties superior to those of other medications, especially superior properties in terms of bronchoprotection and anti-inflammation, and with less secondary side effects.
CGRP is produced in the lung and is released during asthma attacks. We found that it prevents mucosal inflammation and constriction of the tracheobronchial tree in a natural way (see Examples, below). CGRP is therefore a natural substance present in mammalian species (including man), and one of its primary functions at the level of the respiratory tract is to exert a protective effect on the airways and, more specifically, to reduce the intensity of the bronchospasms induced by an asthma crisis. Other advantages attributable to CGRP are that it exercises a non-specific bronchoprotector effect, it does not cause undesirable haemodynamic side effects when administered by inhalation and that it also acts as an anti-inflammatory agent in the lung. CGRP is thus a molecule that highly surpasses everything in the arsenal of therapeutic agents currently available to prevent and attenuate ailments and symptoms associated with asthma.
These and other objects, features and many of the attendant advantages of the invention will be better understood upon a reading of the following detailed description of the invention when considered with the accompanying drawings.